The Role of Dynamic Stabilization and the Aging Spine

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56 The Role of Dynamic Stabilization and the Aging Spine

Reginald J. Davis

KEY POINTS

• The rationale behind posterior motion preservation devices is explained.
• Devices for specific clinical indications are shown.

Introduction

Posterior dynamic stabilization of the lumbar spine is an evolving field. At the core is the concept of incremental stabilization or progressive control of motion of the spine. This contrasts with more traditional fusion techniques where stabilization entails rigid fixation with abolition of motion. These goals are achieved with surgical implantation of posteriorly placed devices, often following surgical decompression where indicated. These devices exert varying degrees of motion control at varying anatomical regions of influence, based on design.

It is a rapidly expanding field with a broad spectrum of devices, approaches, materials, and degree of imparted stabilization. Proper discussion of dynamic stabilization can only occur with organizational hierarchy, considering anatomical location, functional impact, intensity of intervention, and targeted goal of intervention. Each will be considered with relationship to the others.

Devices

The devices can be largely grouped into three categories, based on anatomical location of implantation. These categories are interspinous, facet, and pedicle. These discrete anatomical insertion points allow for a targeted intervention with very specific actions and indications. There is sufficient overlap such that a broad spectrum of disease can be treated.

Interspinous Spacers

The spinous processes and the interspinous space are the sites used with increasing frequency in treating spinal conditions. Though few conditions directly affect the spinous process itself, this anatomical location has utility in implant attachment for distraction and stabilization to a significant degree.

The rationales for interspinous devices are several. They distract the neural foramen to reduce nerve root compression. They also share load with the posterior disc, unload the facets, and assist with stability at the operated level. For the most part they are minimally invasive and easily revisable.

These devices are surgically implanted between the spinous processes or within the interlaminar space. In this location they act to control extension, unload the facets, tension the posterior annulus, as well as tension the posterior ligaments. This influence can be enhanced with surgical positioning in more flexion, or after loaded distraction. The resulting kyphosing moment can increase overall volume for neural elements.

X-Stop (Kyphon)

X-Stop is a titanium alloy device that is designed to stop extension (Figure 56-1). The oval spacer conforms to the interspinous space, and the wings prevent lateral migration. It is minimally invasive and inserted laterally, thus preserving the supraspinous ligament. It is designed to be implanted under local anesthesia. In clinical trial, X-Stop was significantly better than nonoperative treatment of lumbar spinal stenosis at 1 and 2 years post-op. The observed success rate was comparable to published reports for decompressive laminectomy, but with considerably lower morbidity.1,5 X-Stop is currently approved by the U.S. Food and Drug Administration (FDA) for use in patients with claudication symptoms from lumbar stenosis. Patients with relief in flexion and who are otherwise comfortable sitting respond well.

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FIGURE 56-1 X-Stop device interspinous spacer (Kyphon).

Wallis (Zimmer Spine)

The Wallis device is a PEEK interspinous spacer secured to the spinous processes using PET bands (Figure 56-2). It is designed to block extension and control flexion. Indications include isolated lumbar intervertebral instability, such as herniated discs, Modic I degenerative lesions, degenerative disc disease at a level adjacent to a previous fusion, and spinal stenosis treated without laminectomy. In long term (13 year) OUS follow-up, the device obviated the need for arthrodesis in 80% of patients.4 The Wallis device is currently undergoing clinical evaluation and is not FDA approved.

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FIGURE 56-2 The Wallis device interspinous spacer (Zimmer Spine).

Diam (Medtronic)

Diam is an interspinous stabilizer composed of a silicone bumper, encased in polyester mesh, and secured with polyester sutures (Figure 56-3). It is inserted with minimal access and minimal tissue disruption. It is designed to resist extension and reduce intradiscal pressure. Indications include restoration of early segmental degeneration, correction of misalignment often seen in discectomy, and stenosis. Diam is currently undergoing clinical evaluation and is not FDA approved.

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FIGURE 56-3 The Diam interspinous stabilizer (Medtronic).

Coflex (Paradigm)

Coflex is a titanium alloy device whose U-shaped body conforms to the interspinous and interlaminar space (Figure 56-4). It acts as a stiff spring, dynamically stabilizing extension. Lateral migration is prevented by wings compressed onto the spinous processes. Indications include lumbar stenosis, adjacent segment disease, recurrent HNP and early symptomatic disc degeneration. In OUS implantation after decompressive laminectomy in degenerative lumbar spinal stenosis, Coflex was found to be less invasive and provided similar clinical outcome in comparison with instrumented fusion.2 Coflex is currently undergoing clinical evaluation and is not FDA approved.

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FIGURE 56-4 The Coflex device (Paradigm).

ExtenSure (NuVasive)

ExtenSure is a PEEK interspinous spacer secured by geometric conformity to the anatomy and the suturing of the supraspinous ligament (Figure 56-5). It is designed to alleviate pseudoclauditory symptoms and radicular symptoms by enlarging the central canal, lateral recess, and foramina. It also decreases or eliminates low back pain by decreasing pressure on arthritic facet joints, degenerative discs, or both. It also restores disc height and foraminal volume. It is indicated in moderate to severe spinal stenosis, degenerative spondylolisthesis, and mild to moderate degenerative scoliosis. ExtenSure is currently undergoing clinical evaluation and is not FDA approved.

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FIGURE 56-5 The ExtenSure interspinous spacer (NuVasive).

In-Space (Synthes)

In-Space is a laterally placed PEEK cylindrical device, secured by deployable wings (Figure 56-6). It is intended to stop segmental extension and to distract the symptomatic interspinous space. In doing so, maintenance of foraminal height, opening of the area of the spinal canal, reduction of stress on the facets, and relieving of pressure on the posterior annulus results. It is indicated in lumbar spinal stenosis, disc protrusions with discogenic low back pain, facet syndrome due to face osteoarthritis, degenerative spondylolisthesis up to grade 1, and degenerative disc disease. In-Space is not FDA approved.

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FIGURE 56-6 The In-Space device (Synthes).

Superion (Vertiflex)

Superion is a titanium alloy interspinous device with deployable wings (Figure 56-7). It is designed for percutaneous implantation in the treatment of moderate degenerative lumbar stenosis at one or two levels. Superion is currently under clinical investigation in the United States and is not FDA approved.

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FIGURE 56-7 The Superion interspinous device (Vertiflex).

Facet Devices

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